THC Not Sensing voltage at times

Hello and sorry for the long post. Trying to keep it short. I tried the search feature here in the Forum but didn’t really find something that appeared similar.

I’m running a Crossfire XL with THC and a Thermal Dynamics Cutmaster 40. I’ve been working with the machine for about three months now.
I have an intermittent problem with THC whereby occasionally FireControl will not sense the arc voltage (missing) during a cut and pause the job to allow for a “retry”. In other words, the job starts cutting and somewhere in the middle of the cutting operation the torch stops cutting but I can hear air during the “torch fire” signal and the Crossfire continues with the cutting operation with no cutting actually taking place. I ran a cut operation yesterday that started out fine and then somewhere in the middle it stopped cutting a section and then the torch started cutting again and finished the final cut (letters and star cut first. Final cut is perimeter).
What I did notice during IHS was the torch pushing down on the metal (16 gauge) and bowing it down and upon torch retract the metal popped back up. I’m thinking this is messing with the pierce and cutting heights after IHS and causing my problem. I’ve been producing large cut operations without any problems but I’m concerned that eventually I’ll run a large design only to have it crap out somewhere in the middle and waste a lot of metal. I’ve checked out my Cutmaster 40 and it’s working fine. I spoke with the OEM to confirm that Pilot arc and the Cutting arc will not initiate if the torch tip is too close to work material. Any solutions? Thanks!

what gauge metal are you cutting?
Light weight metals will flex due to the weight of the Torch/Z Axis during IHS cycle. They will also warp due to heating which will raise the metal higher and, therefore rock during IHS.

You might need to clip the metal down to prevent this. Search the forum for ‘hold down clip’. There was some clever approaches posted a while ago.

One other thing. Do you cut out the inside shapes before cutting the outside? If not, this may be your problem.

16 gauge. I saw some posts on clipping the metal down where the discussion was on deflection. It sounds like they were describing the flexing of the steel during IHS.

Yes. Inside shapes and smallest cuts first then I work my way outwards to the largest cuts.

Isn’t this what you were describing above?

So the cutting stopped at the letters and then resumed when you did the outside cut?

The title of this thread doesn’t match your description of what is happening. If the THC was turned on, it would have stopped the program immediately when the torch went out. The only way for it to continue on after the torch went out, is if the THC is not turned on or not connected.

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Yes. On previous errors in different jobs the operation faulted out and stopped. In this case it didn’t.

That was my thought so I verified THC was activated by watching the display in FireControl for the Z axiz activation during the cuts. It’ll show “under THC control” (or something like that) when the torch height is being adjusted during a cut. The first time this happened the machine sensed the lost arc and paused the operation, provided a reset or retry option to continue (I selected retry) and then picked up where it left off (after I reset the electrode in the torch) and it finished the operation.
Also, I just took a video of the machine during the cut operation. I can see the IHS (torch lowers to material and then raises up to pierce height). Then the torch fires, pierce occurs, and it lowers to cutting height. This time I inspected the cutting area to make sure the material wasn’t flexing when the torch initially comes down in IHS. I think the material flexing down too far during IHS is the cause of my cuts not completing. If the torch pushes down on the material at IHS and then it pops back up during retract the initial pierce height will be too low for the plasma cutter to initiate the pilot arc. At this point the cutting height will also be too low and I think the tip was touching the material.
However, this does not explain why FireControl didn’t stop the operation after the arc was lost.